1. Field of the Invention
The present invention relates to a laminating method and a laminating device for performing lamination for a thermal recording paper.
2. Description of the Related Art
As to thermal recording, there are a heat transfer recording method and a heat sensitive recording method. In the heat transfer recording method, an ink ribbon or an ink sheet is overlapped on a recording paper. The ink ribbon or the ink sheet is pressed and heated by a thermal head from the back thereof to transfer ink on the recording paper. As to the heat transfer recording method, there are a fusion transfer type and a sublimation transfer type. on the other hand, in the heat sensitive recording method, a thermal recording paper in which a heat sensitive color layer is formed on a base member is used. The recording paper is colored by being heated with a thermal head to record an image or the like.
With respect to a color thermal recording paper, as shown in FIG. 4, a color thermal recording paper 1 in which a color layer 7 is superimposed on a base member 2 is well known. The color layer 7 comprises a cyan heat sensitive color layer 3, a magenta heat sensitive color layer 4, an yellow heat sensitive color layer 5 and a protect layer 6. Each of the color layers has different heat sensitivity and the heat sensitivity is highest for the upper layer. Utilizing the difference of the heat sensitivity, the recording is performed from the most upper layer in order, adjusting a range of heat energy of the thermal head. Before the next lower layer is recorded, the recorded color layer is optically fixed by radiating ultraviolet rays so as not to color again. The yellow heat sensitive color layer 5, which is most upper layer, is optically fixed by the ultraviolet rays of 420 nm. The magenta heat sensitive color layer 4 is optically fixed by the ultraviolet rays of 365 nm. For the cyan heat sensitive color layer 3, fixing property is not given because it has low heat sensitivity (coloring point of it is high) and is not colored under normal environment.
In the heat transfer recording of the sublimation transfer type, lamination is carried out in order to reduce discoloration and fading of the recording paper and to protect against damaging a surface of the recording paper. The lamination is carried out in a following manner. A laminate sheet in which heat-softening adhesive agent is spread on a transparent resin sheet is overlapped on the surface of the recording paper. The laminate sheet is pressed by a press roller, being heated with a heater or the like so that the adhesive agent is melted and the laminate sheet is adhered to the surface of the recording paper.
Further, due to the lamination, ruggedness caused on the surface of the recording paper during the printing is covered with the laminate sheet and the surface is smoothed. Accordingly, an advantage that gloss of the surface may be improved is obtained besides the forgoing effect that the surface of the recording paper is protected and the discoloration is reduced.
However, when the lamination as described above is carried out on the thermal recording paper, if the heat-softening adhesive agent is heated at higher temperature than softening temperature, unfixed heat sensitive color layer may be colored. Therefore, there arises a problem in that an image or the like already recorded is injured. Moreover, if the thermal recording paper is heated at high temperature, small bubbles are sometimes generated from the heat sensitive color layer. At this time, the surface of the thermal recording paper becomes a blister state.